The use of a filter to control the cleanliness and moisture levels in electronic enclosures, such as hard disk drives, is known. For example, U.S. Pat. No. 4,863,499 teaches an anti-diffusion chemical breather assembly comprising a body, cover and filter media, the latter impregnated with activated charcoal granules. The body and cover define a sealed, tortuous passage or channel which provides fluid communication between the external environment and the hard disk drive interior.
U.S. Pat. No. 5,417,743 teaches a self-adhesive vent filter absorbent assembly for removing gaseous contaminants from an enclosure. The assembly comprises a layer of polymer film forming a diffusion tube, two adhesive layers, at least one filtration layer and, optionally, an absorbent layer.
U.S. Pat. No. 5,593,482 teaches an adsorbent assembly for removing gaseous contaminants from an enclosure, the assembly having an adhesive layer, an adsorbent layer and a filtering layer. An exterior mounted assembly is also provided having an outer layer containing a metal or metallized material that provides an electromagnetic shield to the enclosure.
U.S. Pat. No. 5,997,614 teaches a filter with a channel layer film defining a channel, a boundary layer mounted to at least a portion of the channel layer film and forming a non-adhesive boundary for the channel, and filter media disposed in fluid communication with the channel. The boundary layer typically includes a non-porous or semi-permeable film. The filter is configured and arranged to provide for flow of at least a portion of a fluid along the channel and into the filter media. The filter is used in a device as a filter over a vent in a housing of the device.
In each of these assemblies, gas passes through a well-defined path or channel before entering or after exiting a filter and/or absorbent. While effective at one level in slowing the diffusion of gas within the assembly, an interest remains in alternative designs and/or reducing the gas diffusion rate within the assembly even more.